Method of making aluminum forgings



Patented July 3, 1945 FORGINGS Kenneth P. Abbe, Longmeadow, Mass.

N Drawing.

Original application January 2,

1943, Serial No. 471,214.. Divided and this application March 17, 1945, Serial No; 583,397

2 Claims.

This invention relates to an improved method in the art of making aluminum forgings. More particularly it relates to an improvement in the heat treating of such forgings.

Aluminum forgings are commonly subjected to a heat treatment by placing them in a heat treating furnace, where they are kept under high heat treating temperatures for the required time. Immediately upon removal from the furnace they are quenched in water and then'dipped in lye and then in nitric acid solutions. It is well known that this treatment commonly produces blisters giving the product a bad complexion. These blisters may be removed by subsequent machining of the surfaces, but in caseswhere the forgings are not machined the blisters form an objectionable blemish to the appearance. This is particularly true of forgings made of aluminum alloy, such as are commonly used in airplane construction, which are heat treated to give them the desired high tensile strength.

It is the object of the present invention to prevent the formation of blisters on aluminum and aluminum alloy forgings resulting from their heat treatment.

This application is a division of my pending application Serial No. 471,214, filed January 2, 1943. In that application I have set forth certain prior art attempts to prevent the formation of blisters on aluminum forgings by creating a chemical atmosphere in the furnaces in which they are heat treated and the practical failure of such attempts as 'well as the possibledanger to the furnace from the chemical atmosphere. ,In the above mentioned application I have disclosed a method of treating aluminum and aluminum alloy forgings which in practice has substantially eliminated blisters resulting from the heat treating of such forgings, the claims of said application being limited to one of the two species of the invention originally disclosed. The present application presents the other of said species which has been found equally efficacious in preventing blister formation.

In carrying out the present'invention I first dip the forgings in lye and nitric acid solutions,

one after the other, and then completely immerse them in a solution of sodium fluorborate in water.

The sodium fiuorborate in powder form is stirred into the water until the powder is completely dissolved. I do not'believe the proportion of sodium fiuorborate is critical. Ten parts by weight of the sodium fiuorborate powder to one hundred parts by weight of water have' been found satis-. factory in commercial 7 practice. I first took enough powder to dissolve in water with the rough idea that its amount should be substantial. That is enough powder was put in the water to be sure the liquid compound would not be all water. In otherwords more than a trace of sodium fluorborat'e in the solution appears effective to reduce or eliminate th formation of blisters resulting from the heat treatment of the forgings. v

The purpose of first dipping the forgings in the lye and nitric acid solutions is to clean them and prepare the surfac of the forgings so that such surfaces will be met by the solution and will receive and hold onto a film of the solution.

The forgings, after they have been withdrawn from the solution are fully dried and the dry forgings are then placed in the furnace and heat treated as desired. When the forgings are removed from the furnace they are g ven the usual subsequent dips in water to quench them, and in lye and nitric acid solutions to clean them after the heat treatment.

The sodium fiuorborate may be any of the commercially available powdered forms of that substance including the compound sold under the trade name Alarco Compound."

The use of my method not only secures far superior results as compared with other prepared methods but avoids any possible damaging action on the furnace inwhich the forgings are heat treated.

wetting aluminum forgings with a water solution containing more than a trace of sodium fluorborate'. drying the forgings, and then heat treating them in a furnace under high heat treating temperatures but without fusion, to give them strength, the said preliminary steps of wetting and drying the forgings with said solution prior to their said heat treatment step being for the purpose of avoiding blisters during said final step.

2. The method which consists in the following steps: cleaning forgings of aluminum which need to be heat treated at high temperatures below the fusion point, the cleaning of the forging being don for the purpose of preparing all their surfaces for wetting prior to the heat treatment, wettin the cleaned surfaces with a liquid solution containing more than a trace of dissolved sodium fiuorborate, drying the wetted surfaces, putting the forgings in the heat treating, furnace, and finishing the treatment all substantially as and for the purpose described.

KENNETH P. ABBE. 

